Microwave dielectric ceramic with low dielectric constant and high thermal expansion coefficient for high-frequency microwave device and preparation method of microwave dielectric ceramic

Abstract

The invention belongs to the field of microwave dielectric ceramic materials, and particularly provides a method for improving the performance of zinc aluminate microwave ceramic based on an LBSCA (Li2O-B2O3-SiO2-CaO-Al2O3) composite sintering aid, so that the prepared zinc aluminate microwave dielectric ceramic material has a low dielectric constant and a high thermal expansion coefficient, and is suitable for manufacturing a ceramic substrate with excellent performance. According to the invention, a Zn < 0.90 > Co < 0.10 > Al < 2 > O < 4 > system is adopted, an LBSCA (Li2O-B2O3-SiO2-CaO-Al2O3) composite sintering aid is introduced, and sintering and dielectric properties are optimized through a plurality of mechanisms. The doping of the LBSCA glass has obvious influence on the microstructure and density of the ceramic, and the microwave dielectric property of the ceramic is further improved. According to the invention, when the sintering temperature is 1175 DEG C and x is equal to 1.5 wt%, the optimal performance is as follows: epsilon r is equal to 5.25, Q * f is equal to 7334 GHz, and tauf is equal to-25.18 ppm / DEG C; the CTE value is the maximum value of 11.18 ppm / DEG C.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave dielectric ceramic materials, and particularly relates to a low dielectric constant-high thermal expansion coefficient microwave dielectric ceramic for high-frequency microwave devices and a preparation method thereof. Background Art

[0002] Low-temperature co-fired ceramic (LTCC) technology realizes the miniaturization and multi-functionality of microwave devices by co-firing ceramics and metal conductors at low temperatures. One of its core requirements is to develop dielectric materials with both low dielectric constants and high thermal expansion coefficients to adapt to the requirements of high-frequency signal transmission and thermal matching for power chip packaging.

[0003] Zinc aluminate (ZnAl2O4) is an inorganic compound with excellent properties and is widely used in fields such as electronics, optics, and catalysis. It has a relatively high dielectric constant and low dielectric loss, showing good electrical properties and being able to maintain stable performance under high-frequency and high-temperature conditions. These characteristics enable it to play an important role in fields such as high-frequency electronic devices, wireless communication, sensors, microwave ceramics, and resonators.

[0004] ZnAlO material has a low dielectric constant (about 8 - 10), which helps to reduce signal loss in high-frequency circuits and makes it perform excellently in high-frequency and low-signal-loss applications. At the same time, the high thermal expansion coefficient of this material (about 8.4×10 -6 / K) enables it to better adapt to thermal stress in an environment with large temperature fluctuations and enhances its stability under high-temperature conditions. Therefore, ZnAlO has unique advantages in high-frequency electronic devices and high-temperature application fields. However, traditional low-temperature sintering processes are difficult to maintain its performance. Therefore, in recent years, by introducing composite sintering aids (such as LiO - B2O3, ZnO - SiO2, etc.) to optimize the sintering process, not only can the sintering temperature be effectively reduced to below 1200 °C, but also a more uniform and dense microstructure can be obtained by regulating grain growth and suppressing the formation of abnormal grains, thereby further reducing the dielectric constant of the material and increasing its thermal expansion coefficient.

[0005] The present invention aims to provide a method for improving the performance of zinc aluminate microwave ceramics based on an LBSCA (Li2O - B2O3 - SiO2 - CaO - Al2O3) composite sintering aid. The prepared ceramic material has a low dielectric constant and a high thermal expansion coefficient and is suitable for manufacturing high-performance ceramic substrates. The present invention is based on the Zn 0.90 Co 0.10 Al2O4 system, adopts an LBSCA composite sintering aid, and synergistically optimizes the sintering behavior and dielectric properties through multiple mechanisms.

[0006] Through the above optimization, the present invention achieves an excellent balance between low dielectric constant (favorable for high-frequency applications) and high thermal expansion coefficient (adaptable to thermally variable environments) in the zinc aluminate microwave ceramic material.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] 1. A low-K-high thermal expansion coefficient zinc aluminate microwave dielectric ceramic for high-frequency microwave devices and a preparation method thereof, characterized by comprising the following steps:

[0009] a. Using ZnO (99%), CoO (99%) and Al2O3 (99%) as raw materials, according to Zn 0.90 Co 0.10 The main powder is obtained by mixing the ingredients in a stoichiometric ratio according to the Al2O4 molecular formula;

[0010] b. The main powder is ball-milled once, taken out and dried after ball milling, and the powder obtained by sieving after drying is placed in a sintering furnace, and heated from room temperature to 1300°C at a heating rate of 2°C / min and kept at this temperature for 3 hours, and then cooled naturally to room temperature with the furnace to obtain the main material;

[0011] c. Add LBSCA (Li2O-B2O3-SiO2-CaO-Al2O3) composite sintering aid to the main material obtained in step b to prepare powder, perform secondary ball milling, and then take out the secondary ball milled material and dry it.

[0012] d. Evenly mix the dried powder with polyvinyl alcohol (PVA) and press into a cylinder (Φ12mm×h 6mm).

[0013] e. The pressed cylindrical body was kept at 510° C. for 2 hours to remove PVA, then heated to 1175° C. at a heating rate of 2° C. / min and sintered for 4 hours to obtain the optimized ZnAl 2 O 4 microwave dielectric ceramic material sample.

[0014] Furthermore, in step b and step c, the first ball milling and the second ball milling both adopt the same wet ball milling, and the wet ball milling is carried out in a planetary ball mill, using deionized water as the solvent and iron balls as the ball milling medium for wet ball milling, wherein the mass ratio of raw materials, solvent and iron balls is 1:1.5:2, the ball milling time is 12 hours, and the ball milling speed is 300r / min.

[0015] Furthermore, in step b and step c, the drying temperature is 80° C. and the drying time is 24 hours.

[0016] Furthermore, in step c, the mass percentage of the sintering aid varies between 0.5% and 2.5 wt % to adjust the dielectric constant and thermal expansion coefficient.

[0017] Furthermore, in step d, the amount of binder is 12 wt%; the sieving process is: sequentially through 40 mesh and 100 mesh, and taking particles between 40 mesh and 100 mesh; the pressure for briquetting is 15 Kg / cm 2 , time is 2 minutes, and pressed into a cylindrical green body.

[0018] Based on the above technical solution, the beneficial effects of the present invention are:

[0019] Doping an appropriate amount of LBSCA glass can effectively reduce the Zn 0.90 Co 0.10 The sintering temperature of Al2O4 microwave dielectric ceramics can be reduced to 1175℃, and the dielectric constant can be reduced to 5.25. In addition, the doping of LBSCA glass has a significant effect on the microstructure and density of the ceramics, which further affects the microwave dielectric properties of the ceramics. With the increase of the doping amount x, Zn 0.90 Co 0.10 ε of Al2O4-x wt% LBSCA ceramics r The changing trend of Q×f value is consistent with that of relative density, both showing a trend of increasing first and then decreasing, indicating that the influence of density on Q×f value is much greater than that of other external factors. f The value also shows a trend of increasing first and then decreasing. In the present invention, when the sintering temperature is 1175℃ and x=1.5wt%, the optimal performance is: ε r =5.25,Q×f=7334GHz,τ f =-25.18ppm / ℃; its CTE value is a maximum of 11.18ppm / ℃. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the X-ray diffraction pattern of the zinc aluminate microwave dielectric ceramic in the embodiment of the invention after sintering at 1175°C.

[0021] Figure 2 This is a scanning electron microscope image of the zinc aluminate microwave dielectric ceramic sintered at 1175°C in the embodiment of the invention.

[0022] Figure 3 is the thermal expansion coefficient of the zinc aluminate microwave dielectric ceramic in the embodiment of the invention after sintering at 1175°C. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and beneficial effects of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0024] Example 1

[0025] This embodiment provides a method for improving the performance of zinc aluminate microwave ceramics based on LBSCA (Li2O-B2O3-SiO2-CaO-Al2O3) composite sintering aid. The chemical formula of the zinc aluminate microwave dielectric ceramic is: Zn 0.90 Co 0.10 Al2O4, specifically including the following steps:

[0026] a. Using ZnO (99%), CoO (99%) and Al2O3 (99%) as raw materials, according to Zn 0.90 Co 0.10 The main powder is obtained by mixing the ingredients in a stoichiometric ratio according to the Al2O4 molecular formula;

[0027] b. Ball milling was performed once according to the mass ratio of main powder: water: iron ball = 1:1.5:2, the ball milling time was 12 hours, the ball milling speed was 300r / min, and the powder was taken out after ball milling and dried at 80℃. After drying, the sieved powder was placed in a sintering furnace, and the temperature was increased from room temperature to 1300℃ at a heating rate of 2℃ / min and kept at this temperature for 3 hours, and then naturally cooled to room temperature along with the furnace to obtain the main material;

[0028] c. Add LBSCA (Li2O-B2O3-SiO2-CaO-Al2O3) composite sintering aid to the main material obtained in step b to form a powder, wherein the mass percentage of the sintering aid is 0.5wt%. The secondary ball milling is performed according to the mass ratio of main powder: water: iron ball = 1:1.5:2, the ball milling time is 12h, and the ball milling speed is 300r / min; then the secondary ball milled material is taken out and dried at 80°C.

[0029] d. The dried powder was uniformly mixed with 12 wt% polyvinyl alcohol (PVA) and pressed into a cylinder (Φ12 mm×h 6 mm) at 20 MPa.

[0030] e. The pressed cylindrical body was kept at 510° C. for 2 hours to remove PVA, then heated to 1175° C. at a heating rate of 2° C. / min and sintered for 4 hours to obtain the optimized ZnAl 2 O 4 microwave dielectric ceramic material sample.

[0031] The zinc aluminate microwave dielectric ceramic material prepared in this embodiment was tested. Among them, the X-ray diffraction pattern is as follows Figure 1 As shown in Figure 2, the crystallinity of ZnAl2O4 in the sample with 0.5wt% LBSCA-1175℃ is good. Figure 2 As shown in the SEM image, the grain size is not uniform. The dielectric constant of the zinc aluminate microwave dielectric ceramic material in this example is 5.14. Figure 3As shown, the thermal expansion coefficient of the zinc aluminate microwave dielectric ceramic material in this example is 10.18, wherein Q×f=5987 GHz, and the resonant frequency temperature stability coefficient is -35.2 ppm / °C.

[0032] Example 2

[0033] This embodiment provides a method for improving the performance of zinc aluminate microwave ceramics based on LBSCA (Li2O-B2O3-SiO2-CaO-Al2O3) composite sintering aid. The chemical formula of the zinc aluminate microwave dielectric ceramic is: Zn 0.90 Co 0.10 Al2O4, specifically including the following steps:

[0034] a. Using ZnO (99%), CoO (99%) and Al2O3 (99%) as raw materials, according to Zn 0.90 Co 0.10 The main powder is obtained by mixing the ingredients in a stoichiometric ratio according to the Al2O4 molecular formula;

[0035] b. Ball milling was performed once according to the mass ratio of main powder: water: iron ball = 1:1.5:2, the ball milling time was 12 hours, the ball milling speed was 300r / min, and the powder was taken out after ball milling and dried at 80℃. After drying, the sieved powder was placed in a sintering furnace, and the temperature was increased from room temperature to 1300℃ at a heating rate of 2℃ / min and kept at this temperature for 3 hours, and then naturally cooled to room temperature along with the furnace to obtain the main material;

[0036] c. Add LBSCA (Li2O-B2O3-SiO2-CaO-Al2O3) composite sintering aid to the main material obtained in step b to prepare a powder, wherein the mass percentage of the sintering aid is 1.0wt%. The secondary ball milling is performed according to the mass ratio of main powder: water: iron ball = 1:1.5:2, the ball milling time is 12h, and the ball milling speed is 300r / min; then take out the secondary ball milled material and dry it at 80°C.

[0037] d. The dried powder was uniformly mixed with 12 wt% polyvinyl alcohol (PVA) and pressed into a cylinder (Φ12 mm×h 6 mm) at 20 MPa.

[0038] e. The pressed cylindrical body was kept at 510° C. for 2 hours to remove PVA, then heated to 1175° C. at a heating rate of 2° C. / min and sintered for 4 hours to obtain the optimized ZnAl 2 O 4 microwave dielectric ceramic material sample.

[0039] The zinc aluminate microwave dielectric ceramic material prepared in this embodiment was tested. Among them, the X-ray diffraction pattern is as follows Figure 1 As shown in Figure 1, the crystallinity of ZnAl2O4 in the sample with 1.0wt% LBSCA-1175℃ is good.Figure 2 As shown in the SEM image, the grain size is relatively uniform, but the porosity is high. The dielectric constant of the zinc aluminate microwave dielectric ceramic material in this example is 5.19. Figure 3 As shown, the thermal expansion coefficient of the zinc aluminate microwave dielectric ceramic material in this example is 10.41, wherein Q×f=5617 GHz, and the temperature stability coefficient of the resonant frequency is -28.2 ppm / °C.

[0040] Example 3

[0041] This embodiment provides a method for improving the performance of zinc aluminate microwave ceramics based on LBSCA (Li2O-B2O3-SiO2-CaO-Al2O3) composite sintering aid. The chemical formula of the zinc aluminate microwave dielectric ceramic is: Zn 0.90 Co 0.10 Al2O4, specifically including the following steps:

[0042] a. Using ZnO (99%), CoO (99%) and Al2O3 (99%) as raw materials, according to Zn 0.90 Co 0.10 The main powder is obtained by mixing the ingredients in a stoichiometric ratio according to the Al2O4 molecular formula;

[0043] b. Ball milling was performed once according to the mass ratio of main powder: water: iron ball = 1:1.5:2, the ball milling time was 12 hours, the ball milling speed was 300r / min, and the powder was taken out after ball milling and dried at 80℃. After drying, the sieved powder was placed in a sintering furnace, and the temperature was increased from room temperature to 1300℃ at a heating rate of 2℃ / min and kept at this temperature for 3 hours, and then naturally cooled to room temperature along with the furnace to obtain the main material;

[0044] c. Add LBSCA (Li2O-B2O3-SiO2-CaO-Al2O3) composite sintering aid to the main material obtained in step b to form a powder, wherein the mass percentage of the sintering aid is 1.5wt%. The secondary ball milling is performed according to the mass ratio of main powder: water: iron ball = 1:1.5:2, the ball milling time is 12h, and the ball milling speed is 300r / min; then take out the secondary ball milled material and dry it at 80°C.

[0045] d. The dried powder was uniformly mixed with 12 wt% polyvinyl alcohol (PVA) and pressed into a cylinder (Φ12 mm×h 6 mm) at 20 MPa.

[0046] e. The pressed cylindrical body was kept at 510° C. for 2 hours to remove PVA, then heated to 1175° C. at a heating rate of 2° C. / min and sintered for 4 hours to obtain the optimized ZnAl 2 O 4 microwave dielectric ceramic material sample.

[0047] The zinc aluminate microwave dielectric ceramic material prepared in this embodiment was tested. Among them, the X-ray diffraction pattern is as follows Figure 1 As shown in Figure 1, the crystallinity of ZnAl2O4 in the sample with 1.5wt% LBSCA-1175℃ is good. Figure 2 As shown in the SEM image, the grain size grows further and tends to be uniform. The dielectric constant of the zinc aluminate microwave dielectric ceramic material in this example is 5.25. Figure 3 As shown, the thermal expansion coefficient of the zinc aluminate microwave dielectric ceramic material in this example is 11.18, wherein Q×f=7334 GHz, and the temperature stability coefficient of the resonant frequency is -25.18 ppm / °C.

[0048] Example 4

[0049] This embodiment provides a method for improving the performance of zinc aluminate microwave ceramics based on LBSCA (Li2O-B2O3-SiO2-CaO-Al2O3) composite sintering aid. The chemical formula of the zinc aluminate microwave dielectric ceramic is: Zn 0.90 Co 0.10 Al2O4, specifically including the following steps:

[0050] a. Using ZnO (99%), CoO (99%) and Al2O3 (99%) as raw materials, according to Zn 0.90 Co 0.10 The main powder is obtained by mixing the ingredients in a stoichiometric ratio according to the Al2O4 molecular formula;

[0051] b. Ball milling was performed once according to the mass ratio of main powder: water: iron ball = 1:1.5:2, the ball milling time was 12 hours, the ball milling speed was 300r / min, and the powder was taken out after ball milling and dried at 80℃. After drying, the sieved powder was placed in a sintering furnace, and the temperature was increased from room temperature to 1300℃ at a heating rate of 2℃ / min and kept at this temperature for 3 hours, and then naturally cooled to room temperature along with the furnace to obtain the main material;

[0052] c. Add LBSCA (Li2O-B2O3-SiO2-CaO-Al2O3) composite sintering aid to the main material obtained in step b to form a powder, wherein the mass percentage of the sintering aid is 2.0wt%. The secondary ball milling is performed according to the mass ratio of main powder: water: iron ball = 1:1.5:2, the ball milling time is 12h, and the ball milling speed is 300r / min; then take out the secondary ball milled material and dry it at 80°C.

[0053] d. The dried powder was uniformly mixed with 12 wt% polyvinyl alcohol (PVA) and pressed into a cylinder (Φ12 mm×h 6 mm) at 20 MPa.

[0054] e. The pressed cylindrical body was kept at 510° C. for 2 hours to remove PVA, then heated to 1175° C. at a heating rate of 2° C. / min and sintered for 4 hours to obtain the optimized ZnAl 2 O 4 microwave dielectric ceramic material sample.

[0055] The zinc aluminate microwave dielectric ceramic material prepared in this embodiment was tested. Among them, the X-ray diffraction pattern is as follows Figure 1 As shown in Figure 2, the crystallinity of ZnAl2O4 in the sample with 2.0wt% LBSCA-1175℃ is good. Figure 2 As shown in the SEM image, the excess liquid phase wraps around the ceramic and inhibits the further growth of the grains, and the grain boundaries become blurred. The dielectric constant of the zinc aluminate microwave dielectric ceramic material in this example is 5.37. Figure 3 As shown, the thermal expansion coefficient of the zinc aluminate microwave dielectric ceramic material in this example is 10.07, wherein Q×f=5760 GHz, and the resonant frequency temperature stability coefficient is -8.7 ppm / °C.

[0056] Example 5

[0057] This embodiment provides a method for improving the performance of zinc aluminate microwave ceramics based on LBSCA (Li2O-B2O3-SiO2-CaO-Al2O3) composite sintering aid. The chemical formula of the zinc aluminate microwave dielectric ceramic is: Zn 0.90 Co 0.10 Al2O4, specifically including the following steps:

[0058] a. Using ZnO (99%), CoO (99%) and Al2O3 (99%) as raw materials, according to Zn 0.90 Co 0.10 The main powder is obtained by mixing the ingredients in a stoichiometric ratio according to the Al2O4 molecular formula;

[0059] b. Ball milling was performed once according to the mass ratio of main powder: water: iron ball = 1:1.5:2, the ball milling time was 12 hours, the ball milling speed was 300r / min, and the powder was taken out after ball milling and dried at 80℃. After drying, the sieved powder was placed in a sintering furnace, and the temperature was increased from room temperature to 1300℃ at a heating rate of 2℃ / min and kept at this temperature for 3 hours, and then naturally cooled to room temperature along with the furnace to obtain the main material;

[0060] c. Add LBSCA (Li2O-B2O3-SiO2-CaO-Al2O3) composite sintering aid to the main material obtained in step b to form a powder, wherein the mass percentage of the sintering aid is 2.5wt%. The secondary ball milling is performed according to the mass ratio of main powder: water: iron ball = 1:1.5:2, the ball milling time is 12h, and the ball milling speed is 300r / min; then take out the secondary ball milled material and dry it at 80°C.

[0061] d. Uniformly mix the dried powder with 12 wt% polyvinyl alcohol (PVA), and press it into a cylinder (Φ12 mm × h 6 mm) under 20 MPa.

[0062] e. Keep the pressed cylindrical green body at 510 °C for 2 hours to remove PVA, then heat it up to 1175 °C at a heating rate of 2 °C / min and sinter for 4 hours to obtain the optimized ZnAl2O4 microwave dielectric ceramic material sample.

[0063] Test the zinc aluminate microwave dielectric ceramic material prepared in this example. Among them, the X-ray diffraction pattern is as Figure 1 shown. In the sample of 2.5 wt% LBSCA - 1175 °C, the crystallinity of ZnAl2O4 is good. As Figure 2 shown in the SEM image, the excessive liquid phase wraps the ceramic and inhibits the further growth of grains, and the grain boundaries are blurred. The dielectric constant of the zinc aluminate microwave dielectric ceramic material in this example is 5.39. As Figure 3 shown, the thermal expansion coefficient of the zinc aluminate microwave dielectric ceramic material in this example is 9.71. Among them, Q×f = 6146 GHz, and the temperature stability coefficient of the resonant frequency is -31.6 ppm / °C.

[0064] Through comparison, it is found that in Example 3, when the sintering temperature is 1175 °C and the mass percentage of the sintering aid is 1.5 wt%, the performance of the obtained sample is the best. Its dielectric constant is 5.25, Q×f = 7334 GHz, the thermal expansion coefficient is 11.18 ppm / °C, and the temperature stability coefficient of the resonant frequency is -25.18 ppm / °C.

[0065] The above is only the specific implementation manner of the present invention. Any feature disclosed in this specification, unless specifically described, can be replaced by other equivalent or similar-purpose alternative features; all the disclosed features, or all the steps in any method or process, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A low-dielectric - high - thermal expansion coefficient zinc aluminate microwave dielectric ceramic for high - frequency microwave devices and its preparation method, characterized in that, It includes the following steps: a. Using ZnO (99%), CoO (99%) and Al2O3 (99%) as raw materials, according to the stoichiometric ratio of the Zn 0.90 Co 0.10 Al2O4 molecular formula for batching, the main powder is prepared; b. The main powder is ball-milled for the first time. After ball-milling, it is taken out and dried. The powder obtained after sieving after drying is put into a sintering furnace and heated from room temperature to 1300 °C at a heating rate of 2 °C / min and held for 3 h, and then naturally cooled to room temperature in the furnace to obtain the main material; c. The LBSCA (Li2O-B2O3-SiO2-CaO-Al2O3) composite sintering aid is added to the main material obtained in step b to form a powder, which is ball-milled for the second time, and then the second ball-milled material is taken out and dried. d. The dried powder is uniformly mixed with polyvinyl alcohol (PVA) and pressed into a cylinder (Φ12 mm × h 6 mm). e. The pressed cylindrical blank is held at 510 °C for 2 hours to remove PVA, and then heated to 1175 °C at a heating rate of 2 °C / min and sintered for 4 hours to obtain the optimized ZnAl2O4 microwave dielectric ceramic material sample.

2. The method for improving the performance of zinc aluminate microwave ceramics based on the LBSCA sintering aid according to claim 1, characterized in that, In steps b and c, the first ball-milling and the second ball-milling both adopt the same wet ball-milling. The wet ball-milling is carried out in a planetary ball mill, and deionized water is used as the solvent and iron balls are used as the ball-milling medium for wet ball-milling. Among them, the mass ratio of the raw material, the solvent and the iron balls is 1:1.5:2, the ball-milling time is 12 hours, and the ball-milling speed is 300 r / min.

3. The method for improving the properties of zinc aluminate microwave dielectric ceramics based on the LBSCA sintering aid according to claim 1, characterized in that In steps b and c, the drying temperature is 80 °C and the drying time is 24 hours.

4. The method for improving the performance of zinc aluminate microwave dielectric ceramics based on the LBSCA sintering aid according to claim 1, wherein, In step c, the mass percentage of the sintering aid varies between 0.5% and 2.5 wt% to adjust the dielectric constant and the thermal expansion coefficient.

5. The method for improving the properties of zinc aluminate microwave dielectric ceramics based on the LBSCA sintering aid according to claim 1, characterized in that, In step d, the dosage of the binder is 12 wt%; the sieving process is as follows: sieving through 40 mesh and 100 mesh in sequence, and taking the particles between 40 mesh and 100 mesh; the pressure for briquetting is 15 Kg / cm 2 , and the time is 2 minutes, and a cylindrical green body is pressed.

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